Method For Monitoring a Yarn Transforming Process

ABSTRACT

At least one yarn is unspooled from at least one bobbin using a spindle cap. The unspooling speed and, in a coordinated manner, other parameters associated with the transformation process, are adjusted according to a quantity representative of the amount of yarn remaining wound on the at least one bobbin, so that the unspooling speed remains below limits imposed by unspooling conditions.

The invention relates to the technical field of the transformation of continuous elongated materials, in particular, textile yarns, which are designated here below as “yarn”, such as, for example, methods for twisting, for single, double or multiple twist.

More particularly, the invention relates to transformation processes in which the yarn is unspooled from a feed bobbin, passed through a spindle which twists it upon itself, while being delivered to a member placed downstream, for example a delivery member and/or a rewind spooling system, or even to another transformation process. The combination of the unspooling, twisting, delivery, rewinding system means constitutes a transformation unit, which is designated herebelow as “working position”, each working position being independent of or associated with other adjacent working positions.

In certain cases, the transformation process is limited by the unspooling conditions of the feed bobbin or bobbins. In general, the diameter of the bobbin decreases as the unspooling proceeds, thereby affecting the yarn unspooling conditions on the periphery of the bobbin. In fact, for a given delivery speed, the rotation of the unspooling point around the bobbin, that is, the point where the yarn leaves the periphery of the bobbin, accelerates as the bobbin diameter decreases, thereby increasing, for example, the unspooling tensions, the irregularity of these tensions, and also the twisting of the yarn upon itself due to this rotation. This influence may affect the quality of the transformation process and/or limit its performance.

Such an influence is particularly important for multiple twisting processes, in particular for double twisting processes. Reference can be made to FIG. 1 to understand the principle thereof, which is recalled here, and which is known to a person skilled in the art.

A feed bobbin (2), formed by the winding of a yarn (1) around a hollow spindle, is placed in a support (3) itself supported by the pin of a spindle (4). This support (3) is coaxially subjected to the pin of the spindle (4) by means such as ball bearings, and it is prevented from rotating about itself by retaining means acting by gravity, or by a magnetic or mechanical force, so that the bobbin (2) and its support (3) do not rotate.

The yarn (1) unspooled from the bobbin (2) is introduced into a channel made in the pin of the spindle (4), and exits via an orifice (5) opening radially in a cylindrical or conical zone called reserve (6) placed below the support of the bobbin (3). The yarn winds a few fractions of turns on the reserve (6) then forms an arc circumventing the bobbin (2) and its support (3), to meet a fixed thread guide (7), before being pulled by downstream members (8, 9) at a given speed V (delivery speed). The downstream members often consist of a pre-delivery member (8), designed to decrease the yarn tension, and a positive delivery member (9), the latter guaranteeing the speed V.

Thanks to the rotation of the spindle (4), the yarn (1) rotates about the bobbin (2) and its support (3) forming a “balloon”. The rotation causes the first twisting of the yarn on itself between the inlet of the spindle and its radial orifice (5) and a second twisting of the yarn on itself between the radial orifice (5) and the fixed thread guide (7). Thus, if the spindle rotates at N rev/min and if the yarn is pulled at V metres/min, in each minute the yarn receives 2 N twists distributed over V metres, or 2N/V twists per metre.

The stability of the process is based on the balance between the tension due to the centrifugal force created by the rotation of the balloon, and the yarn retaining force between the feed bobbin and the said balloon. This retaining force is distributed between the unspooling forces, the friction of the yarn in the winding on the reserve, and auxiliary braking means.

When the unspooling is performed using a device called “spindle cap” by a person skilled in the art, experience shows that the forces generated by the unspooling of the bobbin are mainly associated with the rotation of the yarn unspooling between the periphery of the bobbin and the pin of the spindle and, for a given delivery speed, tend to increase as the bobbin is emptied, that is, as its outside diameter decreases.

As shown in FIG. 1, the spindle cap is formed of an arm (10) which can rotate freely about the pin of the spindle (4) and carries a thread guide (11) at its end. The yarn (1) passes through the thread guide (11), which has the effect of eliminating the friction of the yarn along the periphery and the side of the bobbin.

The “spindle cap” (10) rotates at the same time as the yarn (1) to accompany it in its unspooling, this rotation generally being braked by a friction, magnetic or other device, supplying a resistive torque intended to generate the braking force necessary for the equilibrium of the process.

In fact, for a given resistive torque, the yarn tension necessary to make the spindle cap (10) rotate increases as the outside diameter of the bobbin decreases, due to the decrease in the lever arm which corresponds to the radius of the bobbin (2). In consequence, as the diameter of the bobbin (2) decreases, the yarn tension (1) at the spindle inlet increases, modifying the equilibrium of the forces, the winding of the yarn in the reserve decreasing to a threshold which can cause the yarn to break.

At the same time, the speed of the spindle cap increases, thereby increasing the undesirable losses by friction and vibrations, and affects the stability of the system, giving rise to the possibility of reaching unacceptable limits from the textile or mechanical standpoint.

To solve this problem, the production speed is limited so that the speed of rotation of the spindle cap and/or the tensions generated by the unspooling remain below permissible values, while observing that this speed or these limit tensions are only reached at the end of unspooling of the feed bobbin.

To try to correct these drawbacks, as it appears from patents EP1045053 and JP200307933, means have been proposed for motorizing the spindle cap. These solutions are complex to implement and particularly costly.

In connection with the object of the present invention, a device and a method have been found for monitoring a yarn transforming process which serve to solve this problem rationally and to obtain a significant increase in the productivity of the yarn transformation installations, particularly in the case of twisting processes such as double twist, in which the unspooling is carried out using a spindle cap.

According to the invention, the method for monitoring the process consists in adjusting the unspooling speed and, in a coordinated manner, the other parameters associated with the transformation process, as a function of a quantity representative of the amount of yarn remaining wound on at least one of the bobbins, so that the said unspooling speed remains below the limits imposed by the unspooling conditions on the said bobbin.

According to the invention, the quantity representative of the amount of yarn remaining wound on a bobbin may be its diameter, its weight, its mass, the length of yarn wound on the bobbin, or any other quantity, which can be obtained for example by:

-   -   a direct or indirect measurement of the diameter of the bobbin;     -   a direct or indirect measurement of the weight of the bobbin;     -   a direct or indirect measurement of the speed of rotation of the         yarn around the periphery of the bobbin, or of the spindle cap         which rotates at the same time as the yarn;     -   a quantity determined from a value initialized at the start of         the unspooling (full bobbin), and decremented as a function of         the time according to a pre-programmed law, or as a function of         a representative quantity of the variation in this quantity;         a quantity determined from a value initialized at the start of         the unspooling (full bobbin), and decremented as a function of         the measurement and/or computation of the amount of yarn         unspooled, or as a function of a representative quantity of the         unspooling speed.

According to a preferred embodiment of the invention, the combination of means implemented for the transformation of a yarn (unwinding, spindle, delivery means, etc.) constitute a self-contained working position, that is, these members are individually controlled by independent means, so that the transformation process parameters can be adjusted as a function of a quantity representative of the amount of yarn remaining wound on at least one of the bobbins used in working position, independently of the status of the adjacent working positions.

According to a particularly advantageous embodiment of the invention applied to twisting processes using a spindle, the process monitoring method consists in:

-   -   controlling the speed of rotation of the spindle and the speed         of traction of the yarn by one or more independent means, in a         constant ratio, in order to give the yarn a constant twist per         metre;     -   adjusting the speed of rotation of the spindle (and hence         proportionally the speed of traction) as a function of a         quantity representative of the amount of yarn remaining wound on         the feed bobbin.

According to this application, the law of variation of the speed of rotation of the spindle (and proportionally the speed of traction) as a function of the amount of yarn remaining wound on the feed bobbin, comprises a substantially constant zone between the initial amount of the full bobbin and an intermediate amount, and a substantially decreasing zone between the said intermediate amount and the minimum amount (or zero) at the end of unspooling.

Another problem that the invention proposes to solve is to compensate for the variation in twisting of the yarn resulting from the acceleration of the rotation of the unspooling point around the bobbin as its diameter decreases.

To solve such a problem, according to one embodiment, the speed of rotation of the spindle and the speed of traction of the yarn are controlled by one or more motorizations independent of those of the adjacent positions, by adjusting the speed of rotation of the spindle and the speeds of the delivery members as a function of a quantity representative of the amount of yarn remaining on the feed bobbin in a variable ratio, thereby conferring on the yarn a variable twist per meter, as a function of the said quantity representative of the amount of yarn remaining on the feed bobbin, in order to compensate for the variations in twist per metre caused by the unspooling as a function of the said diameter.

According to another embodiment, the speed of rotation of the spindle and the speed of traction of the yarn are controlled by one or more motorizations independent of those of the adjacent positions, by adjusting the speed of rotation of the spindle and the speeds of the delivery members as a function of a quantity representative of the amount of yarn remaining on the feed bobbin in a variable ratio, thereby conferring on the yarn a variable twist per meter, and of a law of variation as a function of the said quantity representative of the amount of yarn remaining on the feed bobbin, in order to compensate for the variations in twist per metre caused by the unspooling or respooling operations of the twisting process or the upstream or downstream transformation processes.

The invention is summarized below in greater detail in conjunction with the figures and drawings as follows:

FIG. 1 is a schematic view of a double twist process according to the prior art.

FIG. 2 shows a diagram illustrating the production speed limits as the unspooling of the feed bobbin proceeds, according to the prior art.

FIG. 3 shows a diagram illustrating the production speed limits as the unspooling of the feed bobbin proceeds, according to the invention.

FIG. 4 is a schematic view of an embodiment of the invention applied to the double twist process.

The invention is described here in detail in its application to the double twist process. This exemplary application is non-limiting, and other applications can be considered such as single twist, multiple twist, direct stranding, covering. In general, the invention applies to any yarn transforming process in which at least one yarn is unspooled from at least one bobbin using a spindle cap, in which the variation in the quantity of yarn remaining wound on at least one of the feed bobbins (or the diameter of the said bobbin) gives rise to unspooling conditions which affect the quality or performance of the transformation process.

Reference can be made to FIG. 1 and to the corresponding analysis, the same numerals being resumed in the rest of the description.

In the diagrams shown in FIGS. 2 and 3, the time (t) is plotted on the x-axis and the production speed (V) is plotted on the y-axis. The speed (V) equally represents (to the nearest proportional factor) the speed of the spindle or the delivery speed because, to obtain a given torsion, these two speeds are related by a fixed ratio.

At the start of production (20), the bobbin (2) is full (maximum outside diameter). As production proceeds, the diameter of the bobbin (2) decreases, until the end of the production (21) where it reaches its final value (which is generally close to or equal to the diameter of the empty bobbin).

In general, the production speed (V) is limited by the centrifugal forces generated by the rotation of the balloon. The centrifugal force tends to increase the diameter of the balloon and the tensions in the yarn (1). It is therefore necessary to limit the speed of rotation to remain below a diameter corresponding to the available space (particularly the centreline distance between adjacent spindles). The speed of rotation must also be limited to remain below the tensions acceptable by the yarn (to avoid breaking it or jeopardizing its strength by subjecting it to excessive stresses). This limit depends on the nature and count of the yarn, and on the geometry of the device. It does not depend on the diameter of the feed bobbin (2) and is therefore substantially constant over time. This speed limit is shown by the line (22).

The production speed is also limited by the speed of rotation of the unspooling point, due for example to the change in the resultant unspooling forces which, for a given delivery speed, increase as the diameter of the bobbin (2) decreases. For a given speed of rotation limit or traction force limit, the permissible production speed (corresponding here to the delivery speed) decreases as the diameter of the bobbin (2) decreases and therefore decreases as a function of time. The speed limit is shown by the line (23).

In certain configurations (not shown), the curve of the speed limit due to unspooling (23) may remain above the limit speed (22) due to the rotation of the balloon throughout the time between the start (20) and end (21) of production. In this case, it is possible to set a constant production speed (25), according to the prior art.

In other configurations (shown in FIGS. 2 and 3), the curve of the speed limit due to unspooling (23) falls below the limit due to the rotation of the balloon (22) from a point (24) corresponding to a certain quantity of yarn remaining wound on the bobbin (2). In this case, according to the prior art, it is necessary to set a constant production speed, lower at any point between the start (20) and the end (21) of production than the lowest of the limits. In other words, a constant speed limit (25) is adopted, that is, below the curve (23) at the end (21) of production (FIG. 2).

According to the invention, the process monitoring method consists in:

-   -   controlling the speed of rotation of the spindle (4) and the         speed of the yarn traction means (8, 9, etc.) by one or more         motorizations (12, 13, 14, etc.) independent of those of the         adjacent positions, in a constant speed ratio, in order to give         the yarn a constant twist per metre;     -   adjusting the speed of rotation of the spindle (4) (and hence         proportionally the traction speed) as a function of a quantity         representative of the amount of yarn remaining wound on the feed         bobbin (2).

According to a preferred embodiment, provided as a non-limiting example, the control of the spindle (4) and the traction means (8, 9, etc.) have individual motorizations (12, 13, 14, etc.) controlled by speed variators (15, 16, 17), each receiving a setpoint from a computation unit (18), such as an electronic card, programmable logic controller or other. The data representative of the amount of yarn remaining wound on the bobbin (2) is communicated to the computation unit (18) which modifies the speed setpoints according to the laws of variation as a function of the said quantity.

According to the invention (FIG. 3), the law of variation (26) of the speed of rotation of the spindle (and proportionally the speed of traction) as a function of the amount of yarn remaining wound on the feed bobbin (2), comprises a substantially constant zone between the start of production of the initial amount of the full bobbin and an intermediate amount (24), and a substantially decreasing zone between the said intermediate amount (24) and the minimum amount (or zero) at the end of unspooling (21).

According to another advantageous application of the invention to twisting processes by single twist or by multiple twists, the process control method consists in:

controlling the speed of rotation of the spindle (4) and the speed of traction of the yarn (8, 9, etc.) by one or more motorizations (12, 13, 14, etc.) independent of those of the adjacent positions, by adjusting the speed of rotation of the spindle (4) and the speeds of the yarn delivery members (8, 9, etc.) as a function of a quantity representative of the amount of yarn remaining wound on the feed bobbin (2) in a variable ratio, thereby conferring on the yarn a variable twist per meter, in order to compensate for the variations in twist per meter caused on the yarn by the unspooling as a function of the said diameter.

Advantageously, such a compensation consists in establishing a law of variation of the ratio between the delivery speed and the spindle speed in order to compensate for variations in torsion caused by all the rewinding, unspooling and transformation phases upstream or downstream of the twisting process.

According to another application of the invention to twisting processes by multiple twist, the process control method consists in:

-   -   controlling the speed of rotation of the spindle (4) and the         speed of the delivery members of the positive yarn (9) by one or         more means (12, 14, etc.) independent of those of the adjacent         positions, in a constant ratio between the speed of the spindle         (4) and the positive delivery and spooling means (9), in order         to give the yarn a constant twist per meter;     -   adjusting the speed of rotation of the spindle (4) (and hence         proportionally the speed of traction to ensure a constant twist)         as a function of a quantity representative of the amount of yarn         remaining wound on the feed bobbin (2);     -   adjusting the speed of rotation of the pre-delivery means (8) to         slacken the yarn from the spindle (4) to compensate for the         variations in tension in the balloon due to the variations in         speed of the spindle (4) and thereby to restore a constant         spooling tension.

According to the invention, the quantity representative of the amount of yarn remaining wound on the bobbin (2) may, for example, be:

-   -   A direct or indirect measurement of the said diameter of the         bobbin (2). This measurement can be taken for example by optical         means, by ultrasound or by any other means. The measurement may         be continuous or discrete, that is, detecting the passage         through one or more intermediate diameters, for example, by         electrical cells of which the beam is cut when the bobbin         reaches the said intermediate diameter or diameters.     -   A direct or indirect measurement of the weight of the bobbin.         This measurement can be taken by measuring the weight of the         bobbin alone, or with its support, or by monitoring the weight         of the complete spindle.     -   A direct or indirect measurement of the speed of rotation of the         yarn around the periphery of the bobbin (2), or of the spindle         cap (10), by optical, magnetic or other means.

In the case in which the balloon surrounds the bobbin (2) and its support (3), the measurement means mentioned above may be placed outside the said support and outside the balloon formed by the yarn. They may also be mounted with the bobbin (2) or its support (3) inside the said balloon, in which case, the data may be transmitted by any infrared, radiofrequency or other means.

According to the invention, the quantity representative of the amount of yarn remaining wound on the bobbin (2) may also be determined by a computation, from data representative of the variation in this quantity. For example, for a given production speed, this quantity of yarn on the feed bobbin decreases in accordance with the weight or length removed per unit of time. Thus, the amount of yarn remaining wound on the bobbin and hence the variation in its weight and/or in its diameter, can be calculated, for example, from:

-   -   a quantity determined from a value initialized at the start of         the unspooling (full bobbin), and decremented as a function of         the time according to a pre-programmed law;     -   a quantity determined from a value initialized at the start of         the unspooling (full bobbin), and decremented as a function of         the measurement and/or computation of the amount of yarn         unspooled.

The calculation can be carried out in the computer (18) or by any other external means and communicated thereto, for example by a network (19).

The determination of the quantity representative of the amount of yarn remaining wound on the bobbin, the calculation of the production speed and its transmission to the means for monitoring the members, particularly the spindle (4) and the delivery system (8, 9, etc.) may be provided by all appropriate means such as computers (18) or electronic circuits, a programmable logic controller or other, associated with sensors, metering systems, etc.

The advantages clearly appear from the description.

Thanks to the invention, it is possible to optimize the process and particularly the production speed, throughout production. It is in particular possible to minimize the consequences of limitations resulting from factors inherent in the unspooling and which only act for certain bobbin diameters, for example at the end of unspooling.

The invention can be applied to machines equipped with collective motorization means. It is extremely advantageous for machines consisting of self-contained working positions, that is, equipped with individual motorization means. In fact, each working position is thus monitored to obtain the optimal production speed, according to the state of unspooling of its own bobbin. 

1. Method for monitoring a yarn transforming process in which at least one yarn is unspooled from at least one feed bobbin using a spindle cap mounted rotating freely while being driven by said at least one yarn, in which variation in quantity of yarn remaining wound on the at least one feed bobbin or a diameter of said at least one feed bobbin gives rise to unspooling conditions which affect equality or performance of the transforming process, wherein unspooling speed and, in a coordinated manner, other parameters associated with the transforming process, are adjusted according to a quantity representative of an amount of yarn remaining wound on the at least one bobbin, so that the unspooling speed remains below limits imposed by the unspooling conditions.
 2. Method according to claim 1, wherein the representative quantity is obtained by a direct or indirect measurement of the diameter of the at least one feed bobbin.
 3. Method according to claim 1, wherein the representative quantity is obtained by a direct or indirect measurement of weight of the at least one feed bobbin.
 4. Method according to claim 1, wherein the representative quantity is obtained by a direct or indirect measurement of speed of rotation of the yarn around a periphery of the at least one feed bobbin, or of the spindle cap which rotates at a same time as the yarn.
 5. Method according to claim 1, wherein the representative quantity is determined from a value initialized at a start of the unspooling, and decremented as a function of time according to a pre-programmed law, or as a function of a representative quantity of a variation in said quantity.
 6. Method according to claim 1, wherein the representative quantity is determined from a value initialized at the start of the unspooling, and decremented as a function of measurement and/or computation of amount of yarn unspooled, or as a function of a representative quantity of the unspooling speed.
 7. Use of the method according to claim 1, for a method of single twist, double twist, stranding, or covering of yarns in which the at least one yarn is unspooled from the at least one bobbin using the spindle cap mounted rotating freely while being driven by the yarn and using at least one spindle, wherein: speed of rotation of the spindle and speed of traction of the yarn are controlled by one or more independent means, in a constant ratio, in order to give the yarn a constant twist per metre; the speed of rotation of the spindle and hence proportionally the speed of traction is adjusted as a function of a quantity representative of the amount of yarn remaining wound on the at least one feed bobbin.
 8. Use of the method according to claim 1, for a method of single twist, double twist, stranding, or covering of yarns in which the at least one yarn is unspooled from the at least one feed bobbin using a spindle cap mounted rotating freely while being driven by the yarn and using at least one spindle, wherein speed of rotation of the spindle and speeds of delivery members of the yarn are controlled by one or more motorizations independent of adjacent positions, while adjusting the speed of rotation of the spindle and the speeds of said delivery members as a function of a quantity representative of the amount of yarn remaining wound on the feed bobbin in a variable ratio, thereby conferring on the yarn a variable twist per metre, in order to compensate for variations in twist per metre caused by the unspooling as a function of said diameter.
 9. Use of the method according to claim 1, for a method of single twist, double twist, stranding, or covering of yarns in which the at least one yarn is unspooled from the at least one bobbin using a spindle cap mounted rotating freely while being driven by the yarn and using at least one spindle, wherein: speed of rotation of the spindle and speed of delivery members of the yarn are controlled by one or more means independent of adjacent positions, in a constant ratio between the speed of the spindle and the delivery members, in order to give the yarn a constant twist per meter; the speed of rotation of the spindle and hence proportionally speed of traction is adjusted as a function of a quantity representative of the amount of yarn remaining wound on the feed bobbin; the speed of rotation of pre-delivery means is adjusted to slacken the yarn from the spindle to compensate for variations in tension in a balloon due to the variations in speed of the spindle and thereby to restore a constant spooling tension.
 10. Use of the method according to claim 7, wherein speed is controlled in accordance with a law of variation of the speed of rotation of the spindle and proportionally the speed of traction as a function of the amount of yarn remaining wound on the feed bobbin, the law comprising a substantially constant zone between an initial amount of a full bobbin and an intermediate amount, and a substantially decreasing zone between the intermediate amount and a minimum amount or zero at an end of unspooling.
 11. Device for implementing the method according to claim 1, wherein each working position is equipped with members controlled by independent motorizations, so that the transforming process parameters can be adjusted as a function of a quantity representative of an amount of yarn remaining wound on at least one bobbin in the working position, independently of status of adjacent working positions.
 12. Device according to claim 11, wherein monitoring of a spindle and of delivery members having individual motorizations is controlled by speed variators, each variator receiving a speed setpoint from a computation unit.
 13. Device according to claim 12, wherein data representative of the amount of yarn remaining wound on the bobbin is communicated to the computation unit which modifies each speed setpoint according to laws of variation as a function of the said diameter.
 14. Device according to claim 11, wherein preparation of the quantity representative of the amount of yarn remaining wound on the bobbin, and/or computation of production speed and its transmission to member monitoring means are provided by a computer or an electronic circuit, or a programmable logic controller.
 15. Method for monitoring a transformation process by single twist, double twist or stranding of yarns in which at least one yarn is unspooled from at least one feed bobbin and using at least one spindle, wherein speed of rotation of the spindle and speed of traction of the yarn are controlled by one or more motorizations independent of adjacent positions, by adjusting the speed of rotation of the spindle and speeds of yarn delivery members as a function of a quantity representative of an amount of yarn remaining on the feed bobbin in a variable ratio, thereby conferring on the yarn a variable twist per meter, and of a law of variation as a function of the quantity representative of the amount of yarn remaining on the feed bobbing, in order to compensate for variations in twist per metre caused by unspooling or respooling operations of twisting process or upstream or downstream transformation processes.
 16. Device according to claim 12, wherein the computation unit comprises an electronic card or a programmable logic controller. 